The present invention relates to a multi-component granular additive for polyolefin, the additive containing a specific nucleating agent, a phenolic antioxidant, and polypropylene as essential components, and to a method for producing the additive. The invention also relates to a polyolefin composition containing the additive.
A variety of additives are incorporated into polyolefins, such as a stabilizer for imparting process stability against heat, oxidation, etc. during molding thereof and storage stability of the resultant molded products against light, heat, oxidation, etc.; a modifier for imparting strength, transparency, color, etc. to the molded products; and a catalyst deactivator.
Generally, these additives are used in powder form to polyolefins during molding thereof. However, use of these powdery additives produces airborne dust, which is problematic in terms of operational safety. In addition, a number of additives which differ in terms of specific weight and form must be uniformly mixed in arbitrary proportions, thereby raising problems in weighing and operation.
According to one proposed approach to solve these problems, a number of powdery additives are mixed in arbitrary proportions in advance, and the resultant mixture is shaped into granules. Through granulation, generation of airborne dust can be suppressed, and cumbersome work for formulating and uniformly mixing the additives can be mitigated, to thereby realize so-called dust-free, components-in-granule additives.
Recently, studies are focused on a granulation system employing a dry-compacting apparatus and a pellet mill, and a granulation method making use of a binder such as wax, paraffin, or steramide. However, the above granulation system is unsatisfactory, in that granules produced by means of the system have poor mechanical strength and are readily crushed to fine grains, thereby generating airborne dust, and that uniform mixing cannot be fully attained. In addition, use of a binder results in migration of unwanted compounds into polyolefin.
Japanese Patent Application Laid-Open (kokai) Nos. 5-179056, 6-91152, and 8-333477 disclose mixed granular additives and methods for producing the additives. Although these additives are almost satisfactory in terms of physical properties, functions thereof require improvements. Thus, there still remain problems in relation to integration of additives into granular form.
To crystalline polyolefins; e.g., xcex1-polyolefins such as low-density polyethylene, linear-low-density polyethylene, high-density polyethylene, polypropylene, poly-1-butene, poly-3-methyl-1-butene, and ethylene/propylene block or random copolymers, an antioxidant is added in order to inhibit oxidation during molding and to prevent coloring and deterioration of physical properties. A nucleating agent must also be added to crystalline polyolefins in order to overcome drawbacks thereof; e.g., a slow crystallization rate after heat molding, progress of crystallization after molding, poor strength, and poor transparency. The nucleating agent must be dispersed uniformly in polyolefin resin so as to maximize the effect thereof. However, another problem is that, when the nucleating agent is granulated through the above-mentioned method, the resultant granules have impaired dispersibility, failing to fully attain the effect thereof.
In view of the foregoing, an object of the present invention is to provide a multi-component granular additive for polyolefin, the additive having a strength and functions suitable for serving as a dust-free, components-in-granule additive. Another object is to provide a composition containing polyolefin resin and the additive.
The present inventors have carried out extensive studies in order to solve the aforementioned problems, and have found that the aforementioned problems are effectively solved by a multi-component granular additive for polyolefin, the additive having specific compositional proportions. The present invention has been accomplished on the basis of this finding.
Accordingly, a first invention provides a multi-component granular additive for polyolefin, the additive comprising a nucleating agent that comprises an alkali metal salt or hydroxyaluminum salt of an aromatic monocarboxylic acid or comprises an alkali metal salt or hydroxyaluminum salt of an acid aromatic phosphoric ester compound, in an amount of 10 parts by mass; a phenolic antioxidant in an amount of 1-50 parts by mass; polypropylene in an amount of 5-50 parts by mass; and at least one additive component, serving as an optional component, other than the nucleating agent and the phenolic antioxidant in an amount of 0-500 parts by mass.
A second invention is drawn to a specific embodiment of a multi-component granular additive for polyolefin according to the first invention, wherein the nucleating agent is a compound represented by formula (I): 
wherein n represents 1 or 2; when n is 1, M represents an alkali metal atom; and when n is 2, M represents hydroxyaluminum.
A third invention is drawn to a specific embodiment of a multi-component granular additive for polyolefin according to the first or second invention, wherein the phenolic antioxidant is tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyloxymethyl]methane.
A fourth invention is drawn to a specific embodiment of a multi-component granular additive for polyolefin according to any one of the first to third inventions, wherein said at least one additive component contains a phosphorus-containing antioxidant.
A fifth invention is drawn to a specific embodiment of a multi-component granular additive for polyolefin according to any one of the first to fourth inventions, wherein said at least one additive component contains an alkali metal salt or alkaline earth metal salt of an aliphatic monocarboxylic acid.
A sixth invention is drawn to a specific embodiment of a multi-component granular additive for polyolefin according to any one of the first to fifth inventions, wherein the granular additive has a ratio by mass (percent pulverization) of the particles which pass through a 16-mesh sieve of 1.0% or less as measured in a pulverization acceleration test by use of a shaking apparatus.
A seventh invention provides a method for producing a multi-component granular additive for polyolefin as recited in any one of the first to sixth inventions, characterized by comprising granulating a raw material comprising constitutional components at 150xc2x0 C. to 270xc2x0 C.
The present invention further provides a composition comprising polyolefin resin and the multi-component granular additive for polyolefin according to the first invention.